Transport block size determination

ABSTRACT

Aspects of the present disclosure provide techniques that may be applied in systems comprising machine type communication (MTC) user equipments (UEs). An exemplary method performed by a base station comprises using a first transport block size (TBS) table to communicate with a first type of user equipment (UE), using a second TBS table to communicate with a second type of UE, wherein the first type of UE supports a reduced peak data rate relative to the second type of UE, signaling information to the first type of UE for use in determining a TBS from the first TBS table, and communicating with the first type of UE, with one or more transmissions having a payload with a number of bits determined based on a TBS value from the first TBS table selected based, at least in part, on the signaled information.

CLAIM OF PRIORITY UNDER 35 U.S.C. §119

This application claims benefit of U.S. Provisional Patent ApplicationSer. No. 62/066,300, filed Oct. 20, 2014 and entitled “TRANSPORT BLOCKSIZE DETERMINATION,” which is herein incorporated by reference in itsentirety.

BACKGROUND

I. Field

Certain aspects of the present disclosure generally relate to wirelesscommunications and, more particularly, transport block size (TBS)determination.

II. Background

Wireless communication systems are widely deployed to provide varioustypes of communication content such as voice, data, and so on. Thesesystems may be multiple-access systems capable of supportingcommunication with multiple users by sharing the available systemresources (e.g., bandwidth and transmit power). Examples of suchmultiple-access systems include code division multiple access (CDMA)systems, time division multiple access (TDMA) systems, frequencydivision multiple access (FDMA) systems, 3rd Generation PartnershipProject (3GPP) Long Term Evolution (LTE)/LTE-Advanced systems andorthogonal frequency division multiple access (OFDMA) systems.

Generally, a wireless multiple-access communication system cansimultaneously support communication for multiple wireless terminals.Each terminal communicates with one or more base stations viatransmissions on the forward and reverse links. The forward link (ordownlink) refers to the communication link from the base stations to theterminals, and the reverse link (or uplink) refers to the communicationlink from the terminals to the base stations. This communication linkmay be established via a single-input single-output, multiple-inputsingle-output or a multiple-input multiple-output (MIMO) system.

To enhance coverage of certain devices, such as machine typecommunication(s) (MTC) devices, “bundling” may be utilized in whichcertain transmissions are sent as a bundle of transmissions overmultiple transmission time intervals (TTIs), for example, with the sameinformation transmitted over multiple subframes.

SUMMARY

Certain aspects of the present disclosure provide a method, performed bya base station, for determining a transport block size (TBS) forcommunications involving machine-type-communication user equipments. Themethod generally includes using a first transport block size (TBS) tableto communicate with a first type of user equipment (UE), using a secondTBS table to communicate with a second type of UE, wherein the firsttype of UE supports a reduced peak data rate relative to the second typeof UE, signaling information to the first type of UE for use indetermining a TBS from the first TBS table, and communicating with thefirst type of UE with one or more transmissions having a payload with anumber of bits determined based on a TBS value from the first TBS tableselected based, at least in part, on the signaled information.

Certain aspects of the present disclosure provide an apparatus forwireless communications by a base station. The apparatus generallyincludes means for using a first transport block size (TBS) table tocommunicate with a first type of user equipment (UE), means for using asecond TBS table to communicate with a second type of UE, wherein thefirst type of UE supports a reduced peak data rate relative to thesecond type of UE, means for signaling information to the first type ofUE for use in determining a TBS from the first TBS table, and means forcommunicating with the first type of UE with one or more transmissionshaving a payload with a number of bits determined based on a TBS valuefrom the first TBS table selected based, at least in part, on thesignaled information.

Certain aspects of the present disclosure provide an apparatus forwireless communications by a base station. The apparatus generallyincludes at least one processor configured to use a first transportblock size (TBS) table to communicate with a first type of userequipment (UE), use a second TBS table to communicate with a second typeof UE, wherein the first type of UE supports a reduced peak data raterelative to the second type of UE, signal information to the first typeof UE for use in determining a TBS from the first TBS table, andcommunicate with the first type of UE with one or more transmissionshaving a payload with a number of bits determined based on a TBS valuefrom the first TBS table selected based, at least in part, on thesignaled information; and a memory coupled with the at least oneprocessor.

Certain aspects of the present disclosure provide a computer programproduct for wireless communications by a base station (BS) comprising acomputer readable medium having instructions stored thereon. Theinstructions, when executed by at least one processor, causes the atleast one processor to use a first transport block size (TBS) table tocommunicate with a first type of user equipment (UE), use a second TBStable to communicate with a second type of UE, wherein the first type ofUE supports a reduced peak data rate relative to the second type of UE,signal information to the first type of UE for use in determining a TBSfrom the first TBS table, and communicate with the first type of UE withone or more transmissions having a payload with a number of bitsdetermined based on a TBS value from the first TBS table selected based,at least in part, on the signaled information.

Certain aspects of the present disclosure provide a method, performed bya user equipment, for determining a TBS for communications involvingmachine-type-communication user equipments. The method generallyincludes using a first transport block size (TBS) table to communicatewith a base station (BS), wherein the first TBS table has a reducedmaximum TBS value relative to a second TBS table used by the BS tocommunicate with a second type of UE and wherein the first type of UEsupports a reduced peak data rate relative to the second type of UE,receiving information from the BS for use in determining a TBS from thesecond TBS table, and communicating with the BS, with one or moretransmissions having a payload with a number of bits determined based ona TBS value from the first TBS table selected based, at least in part,on information signaled from the BS.

Certain aspects of the present disclosure provide an apparatus forwireless communications by a base station. The apparatus generallyincludes means for using a first transport block size (TBS) table tocommunicate with a base station (BS), wherein the first TBS table has areduced maximum TBS value relative to a second TBS table used by the BSto communicate with a second type of UE and wherein the first type of UEsupports a reduced peak data rate relative to the second type of UE,means for receiving information from the BS for use in determining a TBSfrom the second TBS table, and means for communicating with the BS, withone or more transmissions having a payload with a number of bitsdetermined based on a TBS value from the first TBS table selected based,at least in part, on information signaled from the BS.

Certain aspects of the present disclosure provide an apparatus forwireless communications by a base station. The apparatus generallyincludes at least one processor configured to use a first transportblock size (TBS) table to communicate with a base station (BS), whereinthe first TBS table has a reduced maximum TBS value relative to a secondTBS table used by the BS to communicate with a second type of UE andwherein the first type of UE supports a reduced peak data rate relativeto the second type of UE, receive information from the BS for use indetermining a TBS from the second TBS table, and communicate with theBS, with one or more transmissions having a payload with a number ofbits determined based on a TBS value from the first TBS table selectedbased, at least in part, on information signaled from the BS; and amemory coupled with the at least one processor.

Certain aspects of the present disclosure provide a computer programproduct for wireless communications by a base station (BS) comprising acomputer readable medium having instructions stored thereon. Theinstructions, when executed by at least one processor, causes the atleast one processor to use a first transport block size (TBS) table tocommunicate with a base station (BS), wherein the first TBS table has areduced maximum TBS value relative to a second TBS table used by the BSto communicate with a second type of UE and wherein the first type of UEsupports a reduced peak data rate relative to the second type of UE,receive information from the BS for use in determining a TBS from thesecond TBS table, and communicate with the BS, with one or moretransmissions having a payload with a number of bits determined based ona TBS value from the first TBS table selected based, at least in part,on information signaled from the BS.

Numerous other aspects are provided including methods, apparatus,systems, computer program products, and processing systems.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram conceptually illustrating an example of awireless communication network, in accordance with certain aspects ofthe present disclosure.

FIG. 2 shows a block diagram conceptually illustrating an example of abase station in communication with a user equipment (UE) in a wirelesscommunications network, in accordance with certain aspects of thepresent disclosure.

FIG. 3 is a block diagram conceptually illustrating an example of aframe structure in a wireless communications network, in accordance withcertain aspects of the present disclosure.

FIG. 4 is a block diagram conceptually illustrating two exemplarysubframe formats with the normal cyclic prefix, in accordance withcertain aspects of the present disclosure.

FIG. 5 illustrates an exemplary subframe configuration for eMTC, inaccordance with certain aspects of the present disclosure.

FIG. 6 illustrates example operations for wireless communications, by abase station (BS), in accordance with certain aspects of the presentdisclosure.

FIG. illustrates example operations for wireless communications, by auser equipment (UE), in accordance with certain aspects of the presentdisclosure.

FIG. 8 illustrates a exemplary TBS table for scheduled broadcasttraffic, in accordance with certain aspects of the present disclosure.

FIGS. 9A and 9B illustrate exemplary TBS tables for eMTC broadcast andunicast, in accordance with certain aspects of the present disclosure.

FIGS. 10A and 10B illustrate exemplary TBS tables for eMTC broadcast andunicast, in accordance with certain aspects of the present disclosure.

FIGS. 11A and 11B illustrate exemplary TBS tables for eMTC broadcast andunicast, in accordance with certain aspects of the present disclosure.

DETAILED DESCRIPTION

Aspects of the present disclosure provide techniques that may helpenable efficient communication between a base station and machine typecommunication (MTC)-based user equipments (UEs). For example, thetechniques may help a UE that supports a reduced peak data rate (e.g.,an MTC UE) to determine a transport block size (TBS) for use incommunication between the UE and its serving base station (BS).

According to certain aspects, a TBS table with a reduced number ofentries (relative to a TBS table for an existing or “legacy” UE type)may be provided. In some cases, a TBS table may have a same number ofentries as a legacy TBS table, but with a reduced maximum TBS. In such acase, the TBS values in the table may not be monotonically increasing.

The techniques described herein may be used for various wirelesscommunication networks such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA andother networks. The terms “network” and “system” are often usedinterchangeably. A CDMA network may implement a radio technology such asuniversal terrestrial radio access (UTRA), cdma2000, etc. UTRA includeswideband CDMA (WCDMA), time division synchronous CDMA (TD-SCDMA), andother variants of CDMA. cdma2000 covers IS-2000, IS-95 and IS-856standards. A TDMA network may implement a radio technology such asglobal system for mobile communications (GSM). An OFDMA network mayimplement a radio technology such as evolved UTRA (E-UTRA), ultra mobilebroadband (UMB), IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20,Flash-OFDM®, etc. UTRA and E-UTRA are part of universal mobiletelecommunication system (UMTS). 3GPP Long Term Evolution (LTE) andLTE-Advanced (LTE-A), in both frequency division duplex (FDD) and timedivision duplex (TDD), are new releases of UMTS that use E-UTRA, whichemploys OFDMA on the downlink and SC-FDMA on the uplink. UTRA, E-UTRA,UMTS, LTE, LTE-A and GSM are described in documents from an organizationnamed “3rd Generation Partnership Project” (3GPP). cdma2000 and UMB aredescribed in documents from an organization named “3rd GenerationPartnership Project 2” (3GPP2). The techniques described herein may beused for the wireless networks and radio technologies mentioned above aswell as other wireless networks and radio technologies. For clarity,certain aspects of the techniques are described below forLTE/LTE-Advanced, and LTE/LTE-Advanced terminology is used in much ofthe description below. LTE and LTE-A are referred to generally as LTE.

A wireless communication network may include a number of base stationsthat can support communication for a number of wireless devices.Wireless devices may include user equipments (UEs). Some examples of UEsmay include cellular phones, smart phones, personal digital assistants(PDAs), wireless modems, handheld devices, tablets, laptop computers,netbooks, smartbooks, ultrabooks, wearables (e.g., smart watch, smartbracelet, smart glasses, smart ring, smart clothing), etc. Some UEs maybe considered machine-type communication (MTC) UEs, which may includeremote devices, such as drones, robots, sensors, meters, location tags,etc., that may communicate with a base station, another remote device,or some other entity. Machine type communications (MTC) may refer tocommunication involving at least one remote device on at least one endof the communication and may include forms of data communication whichinvolve one or more entities that do not necessarily need humaninteraction. MTC UEs may include UEs that are capable of MTCcommunications with MTC servers and/or other MTC devices through PublicLand Mobile Networks (PLMN), for example.

FIG. 1 illustrates an example wireless communication network 100, inwhich aspects of the present disclosure may be practiced. For example,techniques presented herein may be used to help UEs shown in FIG. 1determine a transport block size (TBS) to use when communicating withtheir serving base station (BS).

The network 100 may be an LTE network or some other wireless network.Wireless network 100 may include a number of evolved Node Bs (eNBs) 110and other network entities. An eNB is an entity that communicates withuser equipments (UEs) and may also be referred to as a base station, aNode B, an access point, etc. Each eNB may provide communicationcoverage for a particular geographic area. In 3GPP, the term “cell” canrefer to a coverage area of an eNB and/or an eNB subsystem serving thiscoverage area, depending on the context in which the term is used.

An eNB may provide communication coverage for a macro cell, a pico cell,a femto cell, and/or other types of cell. A macro cell may cover arelatively large geographic area (e.g., several kilometers in radius)and may allow unrestricted access by UEs with service subscription. Apico cell may cover a relatively small geographic area and may allowunrestricted access by UEs with service subscription. A femto cell maycover a relatively small geographic area (e.g., a home) and may allowrestricted access by UEs having association with the femto cell (e.g.,UEs in a closed subscriber group (CSG)). An eNB for a macro cell may bereferred to as a macro eNB. An eNB for a pico cell may be referred to asa pico eNB. An eNB for a femto cell may be referred to as a femto eNB ora home eNB (HeNB). In the example shown in FIG. 1, an eNB 110 a may be amacro eNB for a macro cell 102 a, an eNB 110 b may be a pico eNB for apico cell 102 b, and an eNB 110 c may be a femto eNB for a femto cell102 c. An eNB may support one or multiple (e.g., three) cells. The terms“eNB”, “base station” and “cell” may be used interchangeably herein.

Wireless network 100 may also include relay stations. A relay station isan entity that can receive a transmission of data from an upstreamstation (e.g., an eNB or a UE) and send a transmission of the data to adownstream station (e.g., a UE or an eNB). A relay station may also be aUE that can relay transmissions for other UEs. In the example shown inFIG. 1, a relay station 110 d may communicate with macro eNB 110 a and aUE 120 d in order to facilitate communication between eNB 110 a and UE120 d. A relay station may also be referred to as a relay eNB, a relaybase station, a relay, etc.

Wireless network 100 may be a heterogeneous network that includes eNBsof different types, e.g., macro eNBs, pico eNBs, femto eNBs, relay eNBs,etc. These different types of eNBs may have different transmit powerlevels, different coverage areas, and different impact on interferencein wireless network 100. For example, macro eNBs may have a hightransmit power level (e.g., 5 to 40 Watts) whereas pico eNBs, femtoeNBs, and relay eNBs may have lower transmit power levels (e.g., 0.1 to2 Watts).

A network controller 130 may couple to a set of eNBs and may providecoordination and control for these eNBs. Network controller 130 maycommunicate with the eNBs via a backhaul. The eNBs may also communicatewith one another, e.g., directly or indirectly via a wireless orwireline backhaul.

UEs 120 (e.g., 120 a, 120 b, 120 c) may be dispersed throughout wirelessnetwork 100, and each UE may be stationary or mobile. A UE may also bereferred to as an access terminal, a terminal, a mobile station, asubscriber unit, a station, etc. A UE may be a cellular phone, apersonal digital assistant (PDA), a wireless modem, a wirelesscommunication device, a handheld device, a laptop computer, a cordlessphone, a wireless local loop (WLL) station, a tablet, a smart phone, anetbook, a smartbook, an ultrabook, etc. In FIG. 1, a solid line withdouble arrows indicates desired transmissions between a UE and a servingeNB, which is an eNB designated to serve the UE on the downlink and/oruplink. A dashed line with double arrows indicates potentiallyinterfering transmissions between a UE and an eNB.

FIG. 2 shows a block diagram of a design of base station/eNB 110 and UE120, which may be one of the base stations/eNBs and one of the UEs inFIG. 1. Base station 110 may be equipped with T antennas 234 a through234 t, and UE 120 may be equipped with R antennas 252 a through 252 r,where in general T≧1 and R≧1.

At base station 110, a transmit processor 220 may receive data from adata source 212 for one or more UEs, select one or more modulation andcoding schemes (MCS) for each UE based on CQIs received from the UE,process (e.g., encode and modulate) the data for each UE based on theMCS(s) selected for the UE, and provide data symbols for all UEs.Transmit processor 220 may also process system information (e.g., forSRPI, etc.) and control information (e.g., CQI requests, grants, upperlayer signaling, etc.) and provide overhead symbols and control symbols.Processor 220 may also generate reference symbols for reference signals(e.g., the CRS) and synchronization signals (e.g., the PSS and SSS). Atransmit (TX) multiple-input multiple-output (MIMO) processor 230 mayperform spatial processing (e.g., precoding) on the data symbols, thecontrol symbols, the overhead symbols, and/or the reference symbols, ifapplicable, and may provide T output symbol streams to T modulators(MODs) 232 a through 232 t. Each modulator 232 may process a respectiveoutput symbol stream (e.g., for OFDM, etc.) to obtain an output samplestream. Each modulator 232 may further process (e.g., convert to analog,amplify, filter, and upconvert) the output sample stream to obtain adownlink signal. T downlink signals from modulators 232 a through 232 tmay be transmitted via T antennas 234 a through 234 t, respectively.

At UE 120, antennas 252 a through 252 r may receive the downlink signalsfrom base station 110 and/or other base stations and may providereceived signals to demodulators (DEMODs) 254 a through 254 r,respectively. Each demodulator 254 may condition (e.g., filter, amplify,downconvert, and digitize) its received signal to obtain input samples.Each demodulator 254 may further process the input samples (e.g., forOFDM, etc.) to obtain received symbols. A MIMO detector 256 may obtainreceived symbols from all R demodulators 254 a through 254 r, performMIMO detection on the received symbols if applicable, and providedetected symbols. A receive processor 258 may process (e.g., demodulateand decode) the detected symbols, provide decoded data for UE 120 to adata sink 260, and provide decoded control information and systeminformation to a controller/processor 280. A channel processor maydetermine RSRP, RSSI, RSRQ, CQI, etc.

On the uplink, at UE 120, a transmit processor 264 may receive andprocess data from a data source 262 and control information (e.g., forreports comprising RSRP, RSSI, RSRQ, CQI, etc.) fromcontroller/processor 280. Processor 264 may also generate referencesymbols for one or more reference signals. The symbols from transmitprocessor 264 may be precoded by a TX MIMO processor 266 if applicable,further processed by modulators 254 a through 254 r (e.g., for SC-FDM,OFDM, etc.), and transmitted to base station 110. At base station 110,the uplink signals from UE 120 and other UEs may be received by antennas234, processed by demodulators 232, detected by a MIMO detector 236 ifapplicable, and further processed by a receive processor 238 to obtaindecoded data and control information sent by UE 120. Processor 238 mayprovide the decoded data to a data sink 239 and the decoded controlinformation to controller/processor 240. Base station 110 may includecommunication unit 244 and communicate to network controller 130 viacommunication unit 244. Network controller 130 may include communicationunit 294, controller/processor 290, and memory 292.

Controllers/processors 240 and 280 may direct the operation at basestation 110 and UE 120, respectively, to perform techniques presentedherein for determining a transport block size (TBS) to use forcommunications between a UE (e.g., an eMTC UE) and a base station (e.g.,an eNodeB). For example, processor 240 and/or other processors andmodules at base station 110 may perform direct operations 600 shown inFIG. 6. Similarly, processor 280 and/or other processors and modules atUE 120, may perform or direct operations 700 shown in FIG. 7. Memories242 and 282 may store data and program codes for base station 110 and UE120, respectively. A scheduler 246 may schedule UEs for datatransmission on the downlink and/or uplink.

FIG. 3 shows an exemplary frame structure 300 for FDD in LTE. Thetransmission timeline for each of the downlink and uplink may bepartitioned into units of radio frames. Each radio frame may have apredetermined duration (e.g., 10 milliseconds (ms)) and may bepartitioned into 10 subframes with indices of 0 through 9. Each subframemay include two slots. Each radio frame may thus include 20 slots withindices of 0 through 19. Each slot may include L symbol periods, e.g.,seven symbol periods for a normal cyclic prefix (as shown in FIG. 3) orsix symbol periods for an extended cyclic prefix. The 2L symbol periodsin each subframe may be assigned indices of 0 through 2L−1.

In LTE, an eNB may transmit a primary synchronization signal (PSS) and asecondary synchronization signal (SSS) on the downlink in the center ofthe system bandwidth for each cell supported by the eNB. The PSS and SSSmay be transmitted in symbol periods 6 and 5, respectively, in subframes0 and 5 of each radio frame with the normal cyclic prefix, as shown inFIG. 3. The PSS and SSS may be used by UEs for cell search andacquisition. The eNB may transmit a cell-specific reference signal (CRS)across the system bandwidth for each cell supported by the eNB. The CRSmay be transmitted in certain symbol periods of each subframe and may beused by the UEs to perform channel estimation, channel qualitymeasurement, and/or other functions. The eNB may also transmit aphysical broadcast channel (PBCH) in symbol periods 0 to 3 in slot 1 ofcertain radio frames. The PBCH may carry some system information. TheeNB may transmit other system information such as system informationblocks (SIBs) on a physical downlink shared channel (PDSCH) in certainsubframes. The eNB may transmit control information/data on a physicaldownlink control channel (PDCCH) in the first B symbol periods of asubframe, where B may be configurable for each subframe. The eNB maytransmit traffic data and/or other data on the PDSCH in the remainingsymbol periods of each subframe.

FIG. 4 shows two exemplary subframe formats 410 and 420 with the normalcyclic prefix. The available time frequency resources may be partitionedinto resource blocks. Each resource block may cover 12 subcarriers inone slot and may include a number of resource elements. Each resourceelement may cover one subcarrier in one symbol period and may be used tosend one modulation symbol, which may be a real or complex value.

Subframe format 410 may be used for two antennas. A CRS may betransmitted from antennas 0 and 1 in symbol periods 0, 4, 7 and 11. Areference signal is a signal that is known a priori by a transmitter anda receiver and may also be referred to as pilot. A CRS is a referencesignal that is specific for a cell, e.g., generated based on a cellidentity (ID). In FIG. 4, for a given resource element with label Ra, amodulation symbol may be transmitted on that resource element fromantenna a, and no modulation symbols may be transmitted on that resourceelement from other antennas. Subframe format 420 may be used with fourantennas. A CRS may be transmitted from antennas 0 and 1 in symbolperiods 0, 4, 7 and 11 and from antennas 2 and 3 in symbol periods 1 and8. For both subframe formats 410 and 420, a CRS may be transmitted onevenly spaced subcarriers, which may be determined based on cell ID.CRSs may be transmitted on the same or different subcarriers, dependingon their cell IDs. For both subframe formats 410 and 420, resourceelements not used for the CRS may be used to transmit data (e.g.,traffic data, control data, and/or other data).

The PSS, SSS, CRS and PBCH in LTE are described in 3GPP TS 36.211,entitled “Evolved Universal Terrestrial Radio Access (E-UTRA); PhysicalChannels and Modulation,” which is publicly available.

An interlace structure may be used for each of the downlink and uplinkfor FDD in LTE. For example, Q interlaces with indices of 0 through Q−1may be defined, where Q may be equal to 4, 6, 8, 10, or some othervalue. Each interlace may include subframes that are spaced apart by Qframes. In particular, interlace q may include subframes q, q+Q, q+2Q,etc., where qε{0, . . . , Q−1}.

The wireless network may support hybrid automatic retransmission request(HARQ) for data transmission on the downlink and uplink. For HARQ, atransmitter (e.g., an eNB) may send one or more transmissions of apacket until the packet is decoded correctly by a receiver (e.g., a UE)or some other termination condition is encountered. For synchronousHARQ, all transmissions of the packet may be sent in subframes of asingle interlace. For asynchronous HARQ, each transmission of the packetmay be sent in any subframe.

A UE may be located within the coverage of multiple eNBs. One of theseeNBs may be selected to serve the UE. The serving eNB may be selectedbased on various criteria such as received signal strength, receivedsignal quality, pathloss, etc. Received signal quality may be quantifiedby a signal-to-noise-and-interference ratio (SINR), or a referencesignal received quality (RSRQ), or some other metric. The UE may operatein a dominant interference scenario in which the UE may observe highinterference from one or more interfering eNBs.

As noted above, techniques presented herein may be used to help UEs(e.g., MTC or eMTC UEs) determine a transport block size (TBS) to usewhen communicating with a BS (e.g., an eNodeB).

The focus of traditional LTE design (e.g., for legacy “non MTC” devices)is on the improvement of spectral efficiency, ubiquitous coverage, andenhanced quality of service (QoS) support. Current LTE system downlink(DL) and uplink (UL) link budgets are designed for coverage of high enddevices, such as state-of-the-art smartphones and tablets, which maysupport a relatively large DL and UL link budget.

However, low cost, low rate devices need to be supported as well. Forexample, certain standards (e.g., LTE Release 12) have introduced a newtype of UE (referred to as a category 0 UE) generally targeting machinetype communications or low cost designs, generally referred to asmachine type communication(s) (MTC) UEs. For MTC, various requirementsmay be relaxed as only a limited amount of information may need to beexchanged. For example, maximum bandwidth may be reduced (relative tolegacy UEs), a single receive radio frequency (RF) chain may be used,peak rate may be reduced (e.g., a maximum of 100 bits for a transportblock size), transmit power may be reduced, Rank 1 transmission may beused, and half duplex operation may be performed.

In some cases, if half-duplex operation is performed, MTC UEs may have arelaxed switching time to transition from transmitting to receiving (orreceiving to transmitting). For example, the switching time may berelaxed from 20 μs for regular/legacy UEs to 1 ms for MTC UEs. Release12 MTC UEs may still monitor downlink (DL) control channels in the sameway as regular UEs, for example, monitoring for wideband controlchannels in the first few symbols (e.g., PDCCH) as well as narrowbandcontrol channels occupying a relatively narrowband, but spanning alength of a subframe (e.g., ePDCCH).

Certain standards (e.g., LTE Release 13) may introduce support forvarious additional MTC enhancements, referred to herein as enhanced MTC(or eMTC). For example, eMTC may provide MTC UEs with coverageenhancements up to 15 dB.

As illustrated in the subframe structure 500 of FIG. 5, eMTC UEs cansupport narrowband operation while operating in a wider system bandwidth(e.g., 1.4/3/5/10/15/20 MHz). In the example illustrated in FIG. 5, aconventional legacy control region 510 may span system bandwidth of afirst few symbols, while a narrowband region 530 of the system bandwidth(spanning a narrow portion of a data region 520) may be reserved for anMTC physical downlink control channel (referred to herein as an mPDCCH)and for an MTC physical downlink shared channel (referred to herein asan mPDSCH). In some cases, an MTC UE monitoring the narrowband regionmay operate at 1.4 MHz or 6 resource blocks (RBs).

As noted above, eMTC UEs may be able to operate in a cell with abandwidth larger than 6 RBs. Within this larger bandwidth, each eMTC UEmay still operate (e.g., monitor/receive/transmit) while abiding by a6-physical resource block (PRB) constraint. In some cases, differenteMTC UEs may be served by different narrowband regions (e.g., with eachspanning 6-PRB blocks).

In any case, a transport block size (TBS) for communicating within thisnarrowband region may not be fixed. Thus, a mechanism may be needed toassist a UE, communicating within this narrowband region, to determine aTBS.

In certain systems (e.g., LTE), a transport block size (TBS) isdetermined by using TBS tables that are defined for one layer ormultiple transmission layers. The term layer generally refers to anumber of spatial multiplexing layers, which generally depends on a rankindication (RI) feedback from the UE that identifies how manytransmission layers the UE is able to discern.

Using a TBS table, a base station (e.g., an eNodeB 110) may signalinformation that the UE uses to look up a value from an entry in the TBStable. For example, for broadcast transmissions via a downlink controlinformation (DCI) format 1A, one bit in the DCI may indicate a second orthird column index of the TBS table, while a five-bit MCS in the DCI mayindicate the row index. Additionally, for broadcast transmissions viaDCI format 1C, a separate TBS table may be defined and a five-bit MCS inthe DCI may indicate which entry, out of 32 entries, of the TBS tableshould be used.

According to certain aspects, for unicast transmissions, a number ofassigned RBs may be mapped to a column index and a five-bit MCS may bemapped to a row index. In some cases, the column index may be equal tothe number of assigned RBs. For some special cases (e.g., for specialsubframes in TDD), some scaling may be performed, for example:

column index=alpha*(# of assigned RBs)

where alpha is a scaling value less than 1. In some cases, the MCS toindex row mapping may be many-to-one. That is, there may be cases whentwo or more MCS values map to the same row index. Additionally, in somecases, if the unicast transmission contains a transmission block withtwo or more layers, the TBS may further be determined based on thenumber of layers.

However, for MTC (or eMTC) UEs, certain issues may make it difficult todetermine a TBS. For example, MTC UEs may be expected to support alimited set of transport block sizes. There may also be a limit on amaximum TBS size supported (e.g., 1000 bits, 500 bits, 300 bits, etc.).Additionally, MTC UEs may have certain coverage requirements, forexample, as high at 15 dB. In some cases, TTI bundling operation mayalso be supported by MTC UEs, where a TB is transmitted in multipletransmission time intervals (e.g., over multiple subframes).

Due to these issues, the number of RBs associated with an MTC UE,especially under coverage enhancement (e.g., eMTC), may not serve as agood input parameter for TBS determination. Thus, aspects of the presentdisclosure provide solutions that may be utilized for determining a TBSfor eMTC UEs and help address these issues.

FIG. 6 illustrates example operations 600, performed by a base station(BS) (e.g., BSs 110), for determining a TBS for communications involvingmachine-type-communication user equipments (e.g., eMTC UEs).

Operations 600 begin, at 602 by using a first transport block size (TBS)table to communicate with a first type of user equipment (UE). At 604,the base station uses a second TBS table to communicate with a secondtype of UE, wherein the first type of UE supports a reduced peak datarate relative to the second type of UE. At 606, the base station signalsinformation to the first type of UE for use in determining a TBS fromthe first TBS table. At 608, the base station communicates with thefirst type of UE with one or more transmissions having a payload with anumber of bits determined based on a TBS value from the first TBS tableselected based, at least in part, on the signaled information.

FIG. 7 illustrates example operations 700, performed by a UE (e.g., UE120), for determining a TBS for communications involvingmachine-type-communication user equipments. Operations 700 may beconsidered complementary (UE-side) operations to (BS-side) operations600 shown in FIG. 6.

Operations 700 begin, at 702, by using a first transport block size(TBS) table to communicate with a base station (BS), wherein the firstTBS table has a reduced maximum TBS value relative to a second TBS tableused by the BS to communicate with a second type of UE and wherein thefirst type of UE supports a reduced peak data rate relative to thesecond type of UE. At 704, the UE receives information from the BS foruse in determining a TBS from the second TBS table. At 706, the UEcommunicates with the BS with one or more transmissions having a payloadwith a number of bits determined based on a TBS value from the first TBStable selected based, at least in part, on information signaled from theBS.

The particular content and size of the TBS tables, as well as theinformation used to select a TBS value from such tables, may varyaccording to different aspects.

For example, a TBS table of a limited amount of entries may beassociated with eMTC unicast traffic. For example, a new table may bedefined with limited entries specifically defined for eMTC UEs or thatreuse some entries from existing TBS tables.

As an example, FIG. 8 shows an example of an existing TBS table for DCIformat 1C for scheduled broadcast traffic. FIG. 9A, on the other hand,illustrates a new example TBS table for eMTC broadcast traffic having amaximum TBS of 1000 bits (e.g., less than the maximum TBS for existingTBS tables), which may be based on the 1C table illustrated in FIG. 8with truncation (e.g., with entries above 1000 bits deleted). In otherwords, the TBS table illustrated in FIG. 9A may share a common set ofentries as the TBS table illustrated in FIG. 8 but, in some cases, maytruncate TBSs above 1000 bits. In some cases, the TBS tables illustratedin FIGS. 8 and 9A may (each) be subset of a larger TBS table.

Entries in the example table illustrated in FIG. 9A may be accessed viaa five-bit index (e.g., a five-bit MCS).

As an alternative, rather than simply truncate entries for TBS valuesabove 1000 bits, these entries may be re-used to provide different TBSgranularity. For example, FIG. 9B illustrates an example of a new TBStable for eMTC unicast, which may be based on the 1C table illustratedin FIG. 8, but with different values (below 1000 bits) used in the finalentries. For example, as illustrated in FIG. 8B, TBS indices 24-31 maybe added with corresponding TBS values to provide different TBSgranularity. Again, entries in the example table illustrated in FIG. 9Bmay be accessed via a five-bit index.

In some cases, however, a table may be designed with fewer entriesallowing for a smaller bit index to be used. For example, FIGS. 10A and10B illustrate exemplary new TBS tables for eMTC broadcast and unicast,assuming a max TBS of 300 bits. While the example table of FIG. 10Asimply deletes entries above 300 bits, the example table of FIG. 10Ballows for entries with greater granularity. In either case, by limitingentries to 16 or less, a four-bit index may be sufficient rather thanthe five-bit index needed for TBS tables with more than 16 entries.

FIG. 11A illustrates a exemplary new TBS table for eMTC broadcast, whichmay be based on the 1C table illustrated in FIG. 8 with truncation(relative to existing legacy TBS tables). As illustrated, the tableillustrated in FIG. 11A may be for a four-bit MCS. FIG. 11B illustratesa exemplary new TBS table for eMTC unicast, which based on the 1C tableillustrated in FIG. 8 with modified entries (relative to existing legacyTBS tables). For example, as illustrated, FIG. 11 includes TBS indices24-31 and corresponding TBS values.

Note that the ordering of TBS values for entries of the TBS tablesillustrated in FIGS. 9A-11B is not monotonically increasing. This mayallow for greater reuse of certain portions (e.g., the first entries) ofan existing table (e.g., format 1C table), and betweenbroadcast/unicast.

From the limited (or modified) TBS tables described above, thedetermination of TBS for an eMTC for unicast transmissions may be basedon an explicit index to the TBS table, while the number of RBs assignedto the MTC UES may not be used for TBS determination. That is, a basestation may signal to the UE an explicit index to the TBS table,informing the UE of the TBS to use for transmissions between the UE andthe BS. According to certain aspects, a payload of the transmissions(e.g., a number of bits) between the UE and BS may be determined basedon a TBS value from the TBS table selected based, at least in part, onthe signaled information (e.g., the explicitly signaled index).

In some cases, the base station may determine the explicit index basedon a mapping to the TBS table. Additionally, in some cases, differentmappings may be used for different operating modes of the UE. Forexample, there may be one mapping used for a receiving unicasttransmissions mode while another mapping may be used for a receivingbroadcast transmissions mode. Additionally, there may be differentmappings for a downlink transmission mode versus uplink transmissionmode. It should be noted that the operating modes noted above is not anexhaustive list of operating modes and that other operating modes notlisted may exist.

According to certain aspects, TBS determination may be the same betweenbroadcast and unicast for eMTC UEs. For example, the TBS determinationfor both broadcast and unicast may be based on the same TBS table andthe same indexing approach. According to certain aspects, TBSdetermination for broadcast and unicast may be different (e.g., based ondifferent TBS tables or indexing mechanism). Similarly, TBSdetermination may be the same, or different, for uplink and downlink.

Similarly, TBS determination may be the same, or different, forunicast/broadcast and Multimedia Broadcast Multicast Services (MBMS).According to certain aspects, TBS for MBMS may be determineddifferently, for example, using different indexing or TBS tables (e.g.,MBMS TBS using a legacy TBS table).

According to certain aspects, TBS determination for eMTC UEs may bedependent on whether or not transmission time interval (TTI) bundling isenabled and/or may be dependent on a bundling length, where the bundlinglength indicates a number of subframes over which a payload istransmitted. For example, according to certain aspects, if TTI bundlingis not enabled, a first TBS determination approach may be used, whereasif TTI bundling is not enabled, a second TBS determination approach maybe used. According to certain aspects, the first TBS determinationapproach may involve determining TBS in the same fashion as for regularUEs, where the unicast TBS is determined based on MCS and the number ofassigned RBs. The second TBS determination approach may involvedetermining the TBS based on explicit index to a TBS table of limitedentries.

Additionally, as noted above, the TBS determination may be based on abundling length. For example, if TTI bundling length is small, the firstTBS determination approach above may be use, whereas if the TTI bundlinglength is large, the second TBS determination approach above may beused.

According to certain aspects, if two or more TBS determinationapproaches are associated with unicast traffic, there may be a defaultapproach to use for fallback operation. For example, for fallbackoperation, a common search space scheduled DCI may always be associatedwith a fixed TBS determination scheme, while a UE-specific search spacemay be associated with a TBS scheme based on a configuration or implicitdetermination (e.g., based on TTI bundling).

The various mechanisms described above provide techniques for TBS valuedetermination for UEs (e.g., eMTC UEs) that may support differentmaximum TBS values than existing (legacy UEs). Additionally, aspects ofthe present disclosure may also apply to other use cases. For example,if a regular UE needs to use TTI bundling for coverage enhancement(e.g., certain channels being repeated over a long time), a differentmapping (e.g., one in accordance with the present disclosure) of TBS mayalso be used. Additionally, LTE Release 13 introduces a new narrowbandinternet of things (NB-IOT) work item, which may use one RB as a maximumbandwidth and long bundling. Thus, TBS may be determined in a similarfashion.

As used herein, a phrase referring to “at least one of” a list of itemsrefers to any combination of those items, including single members. Asan example, “at least one of: a, b, or c” is intended to cover: a, b, c,a-b, a-c, b-c, and a-b-c.

The various operations of methods described above may be performed byany suitable means capable of performing the corresponding functions.The means may include various hardware and/or software/firmwarecomponent(s) and/or module(s), including, but not limited to a circuit,an application specific integrated circuit (ASIC), or processor.Generally, where there are operations illustrated in Figures, thoseoperations may be performed by any suitable corresponding counterpartmeans-plus-function components.

For example, means for using, means for signaling, means for receiving,and/or means for communicating may include one or more processors, suchas the transmit processor 220, the controller/processor 240, the receiveprocessor 238, and/or antenna(s) 234 of the base station 110 illustratedin FIG. 2 or the transmit processor 264, the controller/processor 280,the receive processor 258, and/or antenna(s) 252 of the user equipment120 illustrated in FIG. 2.

Those of skill in the art would understand that information and signalsmay be represented using any of a variety of different technologies andtechniques. For example, data, instructions, commands, information,signals, bits, symbols, and chips that may be referenced throughout theabove description may be represented by voltages, currents,electromagnetic waves, magnetic fields or particles, optical fields orparticles, or combinations thereof.

Those of skill would further appreciate that the various illustrativelogical blocks, modules, circuits, and algorithm steps described inconnection with the disclosure herein may be implemented as electronichardware, software/firmware, or combinations thereof. To clearlyillustrate this interchangeability of hardware and software/firmware,various illustrative components, blocks, modules, circuits, and stepshave been described above generally in terms of their functionality.Whether such functionality is implemented as hardware orsoftware/firmware depends upon the particular application and designconstraints imposed on the overall system. Skilled artisans mayimplement the described functionality in varying ways for eachparticular application, but such implementation decisions should not beinterpreted as causing a departure from the scope of the presentdisclosure.

The various illustrative logical blocks, modules, and circuits describedin connection with the disclosure herein may be implemented or performedwith a general-purpose processor, a digital signal processor (DSP), anapplication specific integrated circuit (ASIC), a field programmablegate array (FPGA) or other programmable logic device, discrete gate ortransistor logic, discrete hardware components, or any combinationthereof designed to perform the functions described herein. Ageneral-purpose processor may be a microprocessor, but in thealternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

The steps of a method or algorithm described in connection with thedisclosure herein may be embodied directly in hardware, in asoftware/firmware module executed by a processor, or in a combinationthereof. A software/firmware module may reside in RAM memory, flashmemory, ROM memory, EPROM memory, EEPROM memory, phase change memory,registers, hard disk, a removable disk, a CD-ROM, or any other form ofstorage medium known in the art. An exemplary storage medium is coupledto the processor such that the processor can read information from, andwrite information to, the storage medium. In the alternative, thestorage medium may be integral to the processor. The processor and thestorage medium may reside in an ASIC. The ASIC may reside in a userterminal. In the alternative, the processor and the storage medium mayreside as discrete components in a user terminal.

In one or more exemplary designs, the functions described may beimplemented in hardware, software/firmware, or combinations thereof. Ifimplemented in software/firmware, the functions may be stored on ortransmitted over as one or more instructions or code on acomputer-readable medium. Computer-readable media includes both computerstorage media and communication media including any medium thatfacilitates transfer of a computer program from one place to another. Astorage media may be any available media that can be accessed by ageneral purpose or special purpose computer. By way of example, and notlimitation, such computer-readable media can comprise RAM, ROM, EPROM,EEPROM, flash memory, phase change memory, CD/DVD or other optical diskstorage, magnetic disk storage or other magnetic storage devices, or anyother medium that can be used to carry or store desired program codemeans in the form of instructions or data structures and that can beaccessed by a general-purpose or special-purpose computer, or ageneral-purpose or special-purpose processor. Also, any connection isproperly termed a computer-readable medium. For example, if thesoftware/firmware is transmitted from a website, server, or other remotesource using a coaxial cable, fiber optic cable, twisted pair, digitalsubscriber line (DSL), or wireless technologies such as infrared, radio,and microwave, then the coaxial cable, fiber optic cable, twisted pair,DSL, or wireless technologies such as infrared, radio, and microwave areincluded in the definition of medium. Disk and disc, as used herein,includes compact disc (CD), laser disc, optical disc, digital versatiledisc (DVD), floppy disk and Blu-ray disc where disks usually reproducedata magnetically, while discs reproduce data optically with lasers.Combinations of the above should also be included within the scope ofcomputer-readable media.

The previous description of the disclosure is provided to enable anyperson skilled in the art to make or use the disclosure. Variousmodifications to the disclosure will be readily apparent to thoseskilled in the art, and the generic principles defined herein may beapplied to other variations without departing from the spirit or scopeof the disclosure. Thus, the disclosure is not intended to be limited tothe examples and designs described herein but is to be accorded thewidest scope consistent with the principles and novel features disclosedherein.

What is claimed is:
 1. A method for wireless communications by a basestation (BS), comprising: using at least a first transport block size(TBS) table to communicate with a first type of user equipment (UE);using a second TBS table to communicate with a second type of UE,wherein the first type of UE supports a reduced peak data rate relativeto the second type of UE; signaling information to the first type of UEfor use in determining a TBS from the first TBS table; and communicatingwith the first type of UE with one or more transmissions having apayload with a number of bits determined based on a TBS value from thefirst TBS table selected based, at least in part, on the signaledinformation.
 2. The method of claim 1, wherein the first TBS table andsecond TBS table are each a subset of a larger TBS table.
 3. The methodof claim 1, wherein the information signaled to the first type of UEcomprises an explicit index to the first TBS table.
 4. The method ofclaim 3, wherein: the explicit index is based on a mapping into thefirst TBS table; and different mappings are used for different operatingmodes of the first type of UE.
 5. The method of claim 4, wherein thedifferent operating modes of the first type of UE comprise receivingdownlink transmissions and receiving uplink transmissions.
 6. The methodof claim 4, wherein the different operating modes of the first type ofUE comprise receiving unicast transmissions and receiving broadcasttransmissions.
 7. The method of claim 1, wherein the TBS value from thefirst TBS table is selected, at least in part, based on a transmissiontime interval (TTI) bundling size indicating a number of subframes overwhich a payload is transmitted.
 8. The method of claim 1, wherein thefirst TBS table shares a common set of entries with the second TBStable.
 9. The method of claim 1, wherein the first TBS table has alimited number of entries relative to the second TBS table.
 10. Themethod of claim 9, wherein an index to the first TBS table requires atleast one less bit than an index into the second TBS table.
 11. Themethod of claim 1, wherein a maximum TBS of the first table is less thana maximum TBS of the second table.
 12. The method of claim 1, whereinvalues in the first TBS table do not monotonically increase across allentries.
 13. The method of claim 1, wherein the first TBS table is usedto determine TBS values for at least one of: both downlink and uplinktransmissions; both unicast and broadcast transmissions; or MultimediaBroadcast Multicast Service (MBMS) transmissions.
 14. A method forwireless communications by a user equipment (UE), comprising: using afirst transport block size (TBS) table to communicate with a basestation (BS), wherein the first TBS table has a reduced maximum TBSvalue relative to a second TBS table used by the BS to communicate witha second type of UE and wherein the first type of UE supports a reducedpeak data rate relative to the second type of UE; receiving informationfrom the BS for use in determining a TBS from the second TBS table; andcommunicating with the BS with one or more transmissions having apayload with a number of bits determined based on a TBS value from thefirst TBS table selected based, at least in part, on informationsignaled from the BS.
 15. The method of claim 14, wherein the first TBStable and second TBS table are each a subset of a larger TBS table. 16.The method of claim 14, wherein the information signaled from the BScomprises an explicit index to the first TBS table.
 17. The method ofclaim 16, wherein: the explicit index is based on a mapping into thefirst TBS table; and different mappings are used for different operatingmodes of the UE.
 18. The method of claim 17, wherein the differentoperating modes of the UE comprise receiving downlink transmissions andreceiving uplink transmissions.
 19. The method of claim 17, wherein thedifferent operating modes of the UE comprise receiving unicasttransmissions and receiving broadcast transmissions.
 20. The method ofclaim 14, wherein the TBS value from the first TBS table is selected, atleast in part, based on a transmission time interval (TTI) bundling sizeindicating a number of subframes over which a payload is transmitted.21. The method of claim 14, wherein the first TBS table shares a commonset of entries with the second TBS table.
 22. The method of claim 14,wherein the first TBS table has a limited number of entries relative tothe second TBS table.
 23. The method of claim 22, wherein an index tothe first TBS table requires at least one less bit than an index intothe second TBS table.
 24. The method of claim 14, wherein a maximum TBSof the first table is less than a maximum TBS of the second table. 25.The method of claim 14, wherein values in the first TBS table do notmonotonically increase across all entries.
 26. The method of claim 14,wherein the first TBS table is used to determine TBS values for at leastone of: both downlink and uplink transmissions; both unicast andbroadcast transmissions; or Multimedia Broadcast Multicast Service(MBMS) transmissions.
 27. An apparatus for wireless communications by abase station (BS), comprising: at least one processor configured to usea first transport block size (TBS) table to communicate with a firsttype of user equipment (UE), use a second TBS table to communicate witha second type of UE, wherein the first type of UE supports a reducedpeak data rate relative to the second type of UE, signal information tothe first type of UE for use in determining a TBS from the first TBStable, and communicate with the first type of UE with one or moretransmissions having a payload with a number of bits determined based ona TBS value from the first TBS table selected based, at least in part,on the signaled information; and a memory coupled with the at least oneprocessor.
 28. An apparatus for wireless communications by a userequipment (UE), comprising: at least one processor configured to use afirst transport block size (TBS) table to communicate with a basestation (BS), wherein the first TBS table has a reduced maximum TBSvalue relative to a second TBS table used by the BS to communicate witha second type of UE and wherein the first type of UE supports a reducedpeak data rate relative to the second type of UE, receive informationfrom the BS for use in determining a TBS from the second TBS table, andcommunicate with the BS with one or more transmissions having a payloadwith a number of bits determined based on a TBS value from the first TBStable selected based, at least in part, on information signaled from theBS; and a memory coupled with the at least one processor.